For generations, science fiction writers have designed unreal planets according to scientific principles, often with fascinating results. Hal Clement and Poul Anderson stand out as modern masters of this discipline. Clement created a prototypical alien world, the massively oblate planet Mesklin in Mission of Gravity, along with its centipede-like intelligent inhabitants. Poul Anderson fashioned many diverse planets both in his stories and for the marvelous CONTACT conferences, providing challenging environments for suitably alien beings with whom students would then devise means of communication and cooperation.

Only in the last couple of decades has astronomy caught up with imagination and even begun to exceed it  at least where the peculiarity of real planets is concerned. As of 2010, the Extrasolar Planets Encyclopedia has confirmed 500 planets outside of our solar system, circling other stars  and so it is high time for “Journey to the Exoplanets,” an iPad-compatible app with primary text by Edward Bell and artwork by Ron Miller, published by Scientific American, Farrar, Straus and Giroux, and Brandwidth.

The app has broad appeal. For science and science fiction fans, Miller’s beautiful portraits of dozens of extrasolar planets bring back fond memories of days spent studying the astronomical art of Chesley Bonestell and Ludek Pesek. But the value of “Journey to the Exoplanets” extends beyond beauty and visuals to conceptual tools that allow users to play with the very principles of “planet building,” by choosing prospective star classifications, then sliding bars for a planet’s size and distance from a chosen star, and planet age. The rotating globe in the accompanying display responds to the new parameters and changes accordingly from a brown airless rock to ocean-covered “Goldilocks zone” terrestrial, to ice-bound Neptunian, to immense Jovian gas giant  and back around again, given sufficient time, to a dead, icy hulk.

Click to enlarge

For teachers and students, there’s a “Little Scientist” feature that should appeal to not-so-little scientists as well, guiding us through experiments and measurements that address the kinds of problems astronomers frequently encounter.

Nature has offered up surprises almost beyond science fiction’s imagination. In 1992, Aleksandr Wolszczan and Dale Frail, working at the Arecibo Observatory in Puerto Rico, found a pulsar with an irregular pulse  PSR B1257+12. This hurry-up and fall-behind rotation of the neutron stars’ radiation beacon was caused by at least two planetary bodies, one four times, the other a little more than three times Earth’s mass. Miller depicts planet b with a lovely and likely deadly planetary view of the pulsar itself, its beacon provoking blue and green aurora high in a speculative atmosphere. What an alien environment this must be! It seems unlikely that carbon-based life could arise on a pulsar-orbiting planet, but that doesn’t stop my imagination from racing toward more far-fetched possibilities!

The Gliese 581 system supports multiple planets, some of which could harbor Earthlike life. Miller shows us the lightly forested surface of Gliese 581g at sunrise  or sunset!

Tantalizing glimpses of more Earthlike planets may be given by new instruments and probes, including the Hawaiian Keck Observatory’s amazing “nulling” interferometer, which cancels out star light from an image and leaves only the far fainter reflected light of possible planets. Spectrographic analysis of that light can in turn tell us something about the planet’s components. The presence of oxygen or ozone could point to photosynthesis, and thus an ecosystem similar to our own.

The Kepler spacecraft, launched in 2009, uses a photometer to track the brightness of 145,000 stars. In the first four months of its mission, by February of 2011, Kepler had discovered an amazing 1200 candidate planets.

It appears that planets are far from rare, and that even Earthlike planets may be common  though that is still far from certain.

Bell’s text and sidebars (by scientists and science writers Sarah Seager, John Matson, Lawrence Krauss, and James F. Kasting), give a good overview of both the astronomy, the technology, the history, and the future of exoplanetary discovery.

Click to enlarge

More such apps are doubtless in the works, promising attractive and entertaining ways to gain new enthusiasms and knowledge or re-acquaint with earlier passions. If they’re as excellent as “Journey to the Exoplanets,” I look forward to them all!